The invention relates to new cascade polymer complexes, agents that contain these compounds, the use of the complexes in diagnosis and therapy, and a process for the production of these compounds and agents.
The contrast media that are now used in clinical practice for the modern imaging processes of nuclear spin tomography (MRI) and computer tomography (CT) [Magnevist(copyright), Pro Hance(copyright), Ultravist(copyright) and Omniscan(copyright)] are dispersed in the entire extracellular space of the body (intravascular space and interstitium). This dispersion space comprises about 20% of the volume of the body.
In clinical practice, extracellular MRI contrast media were first used successfully in the diagnosis of cerebral and spinal disease processes since here a quite special situation exists with respect to the regional dispersion space. In the brain and spinal cord, extracellular contrast media in healthy tissue do not leave the intravascular space because of the blood-brain barrier. In the case of pathological processes with disruption of the blood-brain barrier (e.g., malignant tumors, inflammations, demyelinating diseases, etc.), regions with elevated blood-vessel permeability then develop inside the brain for these extracellular contrast media (Schmiedl et al., MRI of Blood-Brain Barrier Permeability in Astrocytic Gliomas: Blood-Brain Barrier Permeability in Astrocytic Gliomas: Application of Small and Large Molecular Weight Contrast Media, Magn. Reson. Med. 22: 288, 1991). Affected tissue can be identified with high contrast relative to healthy tissue by exploiting this disruption of vascular permeability.
Outside of the brain and the spinal cord, however, no such permeability barrier exists for the above-mentioned contrast media (Canty et al., First-Pass Entry of Nonionic Contrast Agent into the Myocardial Extravascular Space. Effects on Radiographic Estimate of Transit Time and Blood Volume. Circulation 84: 2071, 1991). Thus, the concentration of the contrast medium is no longer dependent on vascular permeability, but only on the size of the extracellular space in the corresponding tissue. Delimitation of the vessels relative to the surrounding interstitial space using this contrast medium is not possible.
A contrast medium that is dispersed exclusively in the vascular space would be desirable, particularly for the visualization of vessels. The purpose of such a blood-pool agent. is to make it possible, with the aid of nuclear spin tomography, to delimit tissue with sufficient blood supply from tissue with insufficient blood supply, and thus to diagnose an ischemia. Infarcted tissue can also be delimited, based on its anemia, from surrounding healthy or ischemic tissue if a vasal contrast medium is used. This is of special importance if. e.g., the point is to distinguish a myocardial infarction from an ischemia.
To date, most of the patients in whom there is suspicion of cardiovascular disease (this disease is the most frequent cause of death in Western industrialized countries) have to undergo invasive diagnostic tests. In angiography at present, diagnostic radiology with the aid of iodine-containing contrast media is used in particular. These tests suffer from various drawbacks: they are associated with the risk of radiation exposure, as well as with difficulties and stresses, which therefore particularly have the effect that the iodine-containing contrast media, as compared with NMR contrast media, have to be used in much higher concentrations.
There is therefore a need for NMR contrast media which can mark the vascular space (blood-pool agents). These compounds are to be distinguished by good compatibility and by high effectiveness (high increase of signal intensity with MRI).
Thus far, the attempt to solve at least a part of this problem by using complexing agents that are bound to macromolecules or biomolecules has been successful only to a limited extent.
Thus, for example, the number of paramagnetic centers in the complexes that are described in European Patent Applications No. 0 088 695 and No. 0 150 844 is not sufficient for satisfactory imaging.
If the number of metal ions required is increased by repeated introduction of complexing units into a macromolecular biomolecule, this is associated with an intolerable impairment of the affinity and/or specificity of this biomolecule [J. Nucl. Med. 24, 1158 (1983)].
Macromolecules can generally be suitable as contrast media for angiography. But 24 hours after intravenous injection in rats, albumin-GdDTPA (Radiology 1987; 162: 205), e.g., shows a concentration in the liver tissue that constitutes almost 30% of the dose. In addition, only 20% of the dose is eliminated in 24 hours.
The macromolecule polylysine-GdDTPA (European Patent Application, Publication No. 0 233 619) has also proved suitable as blood-pool agent. Because of production, however, this compound consists of a mixture of molecules of different sizes. In excretion tests in rats, it was shown that this macromolecule is excreted unchanged by glomerular filtration through the kidneys. Due to factors related to synthesis, however, polylysine-GdDTPA may also contain macromolecules that are so large that they cannot pass through the capillaries of the kidneys in the case of glomerular filtration and thus remain in the body.
Also, macromolecular contrast media based on carbohydrates, e.g., dextran, have been described (European Patent Application, Publication No. 0 326 226). The drawback of these compounds lies in the fact that the latter generally carry only about 5% of the signal-enhancing paramagnetic cation.
The polymers described in European Patent Application No. 0 430 863 already represent a step toward blood-pool agents since they no longer exhibit the size and molecular weight relative to heterogeneity that are characteristic of the previously mentioned polymers. They leave something to be desired, however, as regards complete elimination, compatibility, and/or effectiveness.
The object was therefore to make available new diagnostic tools particularly to identify and locate vascular diseases that do not have the above-mentioned drawbacks. This object is achieved by this invention.
It has been found that complexes which consist of nitrogen-containing cascade polymers that are provided with complexing ligands, at least 16 ions of an element of atomic numbers 20-29, 39, 42, 44 or 57-83, and optionally cations of inorganic and/or organic bases, amino acids or amino acid amides, and which optionally contain acylated amino groups are surprisingly very well suited for the production of NMR and x-ray diagnostic agents without exhibiting the mentioned drawbacks.
The complexing cascade polymers according to the invention can be described by general formula I
Axe2x80x94{Xxe2x80x94[Yxe2x80x94(Zxe2x80x94( Wxe2x80x94KW)Z)y]x}axe2x80x83xe2x80x83(I),
in which
A stands for a nitrogen-containing cascade nucleus of base multiplicity a,
X and Y, independently of one another, stand for a direct bond or a cascade reproduction unit of reproduction multiplicity x or y,
Z and W, independently of one another, stand for a cascade reproduction unit of reproduction multiplicity z or w,
K stands for the radical of a complexing agent,
a stands for numbers 2 to 12,
x, y, z and w, independently of one another, stand for numbers 1 to 4,
provided that at least two reproduction units are different and that
16xe2x89xa6axc2x7xxc2x7yxc2x7zxc2x7wxe2x89xa664
holds true for the product of the multiplicities. As cascade nucleus A, the following are suitable: nitrogen atom, 
in which
m and n stand for numbers 1 to 10,
p stands for numbers 0 to 10,
U1 stands for Q1 or E,
U2 stands for Q2 or E with
E meaning the group 
xe2x80x83whereby
o stands for numbers 1 to 6,
Q1 stands for a hydrogen atom or Q2 and
Q2 stands for a direct bond,
M stands for a C1-C10 alkylene chain which optionally is interrupted by 1 to 3 oxygen atoms and/or optionally is substituted with 1 to 2 oxo groups,
Ro stands for a branched or unbranched C1-C10 alkyl radical, a nitro, amino, carboxylic acid group or for 
whereby the number of Q2 elements corresponds to base multiplicity a.
The nitrogen atom, whose three bonds (base multiplicity a=3) in a first xe2x80x9cinner layerxe2x80x9d (generation 1) are occupied by three reproduction units X or Y (if X stands for a direct bond) or Z (if X and Y in each case stand for a direct bond), represents the simplest case of a cascade nucleus; in other words: the three hydrogen atoms of the basic cascade starter ammonia A(H)axe2x95x90NH3 have been substituted by three reproduction units X or Y or Z. In this case, the number of Q2 elements contained in cascade nucleus A represents base multiplicity a.
Reproduction units X, Y, Z and W contain xe2x80x94NQ1Q2 groups, in which Q1 means a hydrogen atom or Q2 and Q2 means a direct bond. The number of Q2 elements contained in the respective reproduction unit (e.g., X) corresponds to the reproduction multiplicity of this unit (e.g., x in the case of X). The product of all multiplicities axc2x7xxc2x7yxc2x7zxc2x7w indicates the number of complexing agent radicals K bound in the cascade polymers. The polymers according to the invention contain at least 16 and at most 64 radicals K in the molecule, which in each case can bond one to a maximum of three (in the case of divalent ions), preferably one, ion of an element of the above-mentioned atomic numbers.
The last generation, i.e., reproduction unit W bound to complexing agent radical K, is bound to K with NH groups (xe2x80x94NQ1Q2 with Q1 meaning a hydrogen atom and Q2=direct bond), while the preceding reproduction units can be linked together both by NHQ2 groups (e.g., by acylation reactions) and by NQ2Q2 groups (e.g., by alkylation reactions).